Preparation for a power outage or a planned power outage at the time of disaster has drawn more attention in recent years. For example, techniques have been studied for supplying power to a residence from a stationary battery system or an electric vehicle to prepare for a power outage at the time of disaster.
Furthermore, it has been known to use a portable power supply in which a battery and an inverter circuit are installed to use electric apparatuses which need commercial power outdoors, etc. (e.g., Patent Literature (PTL) 1).